When a starch has been pre-cooked, it can be used to thicken cold foods. Such a starch is referred to as a pregelatinised or instant starch. Otherwise, starch requires heat to cause it to thicken or “gelatinise”. The actual temperature required to gelatinise starch in an excess of water depends on the type of starch. Pregelatinised starches are particularly widely used in convenience foods such as instant soups, instant sauces, instant gravies, instant beverages, salad dressing mixes and the like, in dairy foods, such as instant puddings and the like, in bakery foods, such as cake mixes, bakery creams and the like, and in instant baby and infant foods.
The terms “gelatinised” or “cooked” starch refers to swollen granules which have lost their polarisation crosses and which may or may not have lost their granular structure. The term “partially gelatinised” starch refers to partially swollen granules which have not yet completely lost their polarisation crosses or their granular structure. The thermal processes generally employed to prepare pregelatinised starches include roll drying, extrusion, high temperature heating in alcohol/water systems and spray cooking/drying. The physical properties of the pregelatinised starches, in particular the wettability, the dispersibility and peak viscosity in cold water, are dependent on the process used to pregelatinise the starch.
Roll-dried and spray cooked/dried starches are the most widely used pregelatinised starches on the market. These starches generally have less thickening power and less gelling tendency than the corresponding granular starch when gelatinised. This loss in thickening and gelling potential is related to the partial destruction of the hydrated granular structure. Roll-dried starches typically have less thickening power compared to spray cooked/dried starches. From a thermodynamic perspective, both common processes, roll drying and spray cooking/drying, are also not very energy efficient. There is therefore a need for starches which have thickening power in cold/warm liquids, which form gels, and which can be produced via a process that is energetically more efficient compared with roll drying and spray cooking/drying techniques.
JP 61-280244 discloses the heat treatment of starch in the presence of superheated steam of temperatures between 105 and 350° C. for less than 5 minutes at gauge-pressures of less than 9 kg/cm2.
WO 2009/013346 relates to a process for modifying starches comprising subjecting a non-pregelatinised starch to a superheated steam treatment.
EP-A-0032296 describes a process and an apparatus for cooking or gelatinising a material in an atomised state, so that there is obtained an easily dryable, uniform and finely-sized product. According to this document, the material which is to be cooked is injected through an atomisation aperture in a nozzle assembly to form a relatively finely-sized spray which is heated in the nozzle assembly to a temperature effective to cook or gelatinise the material in the nozzle assembly.
The process according to the present invention provides cold water-swelling, intact, high amylose starch granules with novel and superior functionalities compared to conventional pregelatinised starches.